External corners need to at least be broken before heat treat, as they too are a stress concentration area. A common misconception is that quench cracks can occur only while the piece is being quenched. Making an improper selection of steel for the process. While large 4140 rounds can be waterquenched, squares are a different story. Aisi 4340 steel is a medium carbon, low alloy steel known for its toughness and strength in relatively large sections. In materials science, quenching is the rapid cooling of a workpiece in water, oil or air to obtain certain material properties. Here are seven ways that steel can fail as a result of quench cracking from heat treatment.
A common misconception is that quench cracks can occur. Yes, even in these days of nanomiracles, steel is still useful and interesting. I still think that after working with it and studying it for 42 years. The quench needs to be fast enough to avoid secondary transformation products, but slow enough to reduce distortion and avoid cracking. Quenchandtempering or heat treating requirements for 1045, 4140, and 4340 plate usually call out a hardness range, but it is not uncommon for an application to require certain mechanical properties beyond hardness. Banding is a naturally occurring condition in any plate steel, and it arises as the ingot or strand cast slab cools from the outside in, which creates a slight variation in grain structure and chemistry. Metal products distributor supplier metals and materials table of contents. The 800 600 400 200 30 oil 60 90 time, s 120 150 o. Quench cracks 3 ways to recognize speaking of precision. From aisi 1045 to aisi 4340 the polymer quenching hardening heat treatment can be the solution for complex jobs.
Analysis of quenching parameters in aisi 4340 steel by. Inservice d2 toolsteel component failure due to quench cracking. The quench cracking that occurs in steels with carbon contents greater than about 0. Best to keep generous radii at all transitions prior to heat treat also. The heat treating process can be an intensely stressful process for the material involved. The martensitic transformation starts at the outermost surfaces of the part being quenched. Quenching oil and heat treatment fluids are designed for rapid or controlled cooling of steel or other metals as part of a hardening, tempering or other heattreating process. Oil quenching thermtech metal heat treating and metal. The whole concept of heat treatment of steel is based on the microstructure of iron. A type of heat treating, quenching prevents undesired lowtemperature processes, such as phase transformations, from occurring. Hence, thegeneralruleofquenchingfromjustabovethecriticalrange.
A very fast cool produces a total martensite grain structure, making a product high in strength but not ductile. Quench cracks 3 ways to recognize quench cracks result from stresses produced during the transition from austenite to martensite, which involves an increase in volume. If the use of water as quenching medium, 4140 steel cooling speed is faster at high temperature range, but the cooling speed is slow at low temperature range lower than the. Continuous mesh belt or roller hearth furnaces with oil or water quench. The material hardenability will determine how severe the quench has to be for a particular part geometry. Quench cracking can appear to be associated with banding in the microstructure of the steel.
Polymer quenching is useful for a wide range of steels. To accomplish this task, we must work with design and manufacturing engineers on materials selection, manufacturing methods including heat treatment and safety allowances. The material must first be heated to the point where austenitization can occur, and then cooled rapidly enough to have the transformation into. Sae aisi 4340 steel properties, heat treatment, equivalent. Before we can start the quenching process we need to heat the steel to a high heat. Overheating during the austenitizing portion of the heat treatment cycle can. Conditions producing cracks in a particular oilhardening steel were determined experimentally. Six pieces of bar stock for each of the four grades of oil hardening steel 01 tool steel, 4140, 4150, and 4340 alloy steels were used for this test. An aisi 4340 threaded steel connecting rod that was part of a connecting linkage used between a parachute and an instrumented drop test assembly frac. December 15, 2009 comments off on heat treatment cracks. Overload failure of a quenchcracked aisi 4340 steel. The influence of chemical composition on the hardenability and quench distortion of automotive components has already been investigated6,7.
It is important for heat treaters to understand the mechanisms associated with quench cracking and to take all prudent steps necessary to avoid inservice product failures fig. When i was in school, i learned that if a piece of steel is cooled too rapidly during the quench portion of a hardening heat treatment, it might crack. This will minimise distortion, cracking and residual stress. Went out to discover a fulllength deep crack in the still very warm bar. Heat treating and brine quench of prepost machined 4340. I suspect that there are lots of commercial heattreat shops quenching 4140 in water in heavy sections, and they know from experience and the graphs and charts in the heat treaters guide that that is necessary. According to the actual production situation, we believe that the main reason of quenching crack of 4140 steel plate is. Throughhardening low alloy steel bar 4340 atlas steels. Sem observation of aisi 4340 steel cooled in water after the heat treatment. Tool designers must also be aware of the problems and difficulties in manufacture, heat treat ment, and use. For materials such as 4340, tempering must take place within 15 minutes of removal from the quench to avoid quench cracking. I specify the heat treating processes used when cutting edge mfg sends something out for treatment. Normal ranges of mechanical properties corresponding to a specific hardness are listed below. Too much time between the quenching and the tempering of the heat treated parts.
The material must first be heated to the point where austenitization can occur, and then cooled rapidly enough to have the. A process for the energy efficient heat treatment of steels wherein a steel workpiece is rapidly heated to a temperature above the a 3 temperature of the steel to convert the steel to austenite, the workpiece is then rapidly quenched in a liquid quench medium to convert the austenite to a predominantly martensitic microstructure, and the steel is then tempered by rapid heating while the. If the steel is an oilhardening steel, the use of these overly aggressive quenchants will lead to cracking. The cring type test is commonly used to investigate the distortion propensity of materials that undergo heat treatment processes such as quenching5. Seven causes for quench cracking in steel failures of steel parts in service or production occur infrequently. Quench cracks usually originate at sharp corners or substantial section size changes. Pdf effect of quenching and tempering treatments on impact.
Highalloy and stainless steels may be quenched to minimize grain boundary carbides or to improve the ferrite. Normalized is steel that has been austenized and allowed to cool in air air quench the quench is very mild and is used to refine the grain structure. Back in the early 1970s, a company down here in houston put in one of the first continous heat treat quench and temper lines. The purpose is to delay the cooling for a length of time to equalise the temperature throughout the piece. Us4404047a process for the improved heat treatment of. Overviewofthemechanismsoffailure in heat treated steel components scott mackenzie, houghton international, inc. Pdf analysis of quenching parameters in aisi 4340 steel by.
Quenching oils and heat treatment fluids selection guide. Aisi 4340 is also one kind of nickel chromium molybdenum steels. It can be avoided by first plating the steel with nickel. If i was faced with this situation and limited by existing air permits, i would instead try to locate a commercial heat treater with oil quenching capability. Alloy description timkensteels 4140hw grade is a finegrained, lowalloy steel that offers optimum heattreat response in heavier crosssections. Jade band marigold introduction atlas 4340 is a nominally 1. It facilitates hardening of steel by controlling heat transfer during quenching. Heres a clip of an aggressive heat treatquenching process designed to allow maximum strength and hardness from this 4340 nickel alloy. Not much practical use other than being a feedstock for heat treating.
Heat to 830 o c 860 o c, hold until temperature is uniform throughout the section, soak for 10 15 minutes per 25 mm section, and quench in oil, water, or polymer as required. Oil quenching bull gears, after case hardening cycle. Oil quenching is a common method for hardening alloy steel forgings. This material at my shop is quenched in 250f agitated oil without any issues. When you oil quench steel forgings, theres also less risk of cracking compared to water quenching or polymer quenching. Interrupted quenching of steels typically in a molten salt bath, at a temperature just above the martensitic phase. Mechanical properties considered as a function of heat treatments conditions and the empirical models were built up for highly. The quenchant used in the electric atmos phere furnace was park aaa quench oil at 0f 1400f 540c 6000. Typical heat treatment defects of gears and solutions. Avoid over heating and overly long dwell times while austenitizing. The high hardness of 4340 alloy steel requires that the material be welded in the annealed or tempered state and then heat treated to.
Throughhardening low alloy steel bar 4340 colour code. Overheating during the austenitizing portion of the heat treatment cycle can coarsen normally fine grained steels. However, when steel parts fail, the consequences are dire. Since 4340 alloy steel is air hardened, the welded parts should be either annealed or normalized and tempered shortly after welding. This is to reduce likelihood of cracking during quench. Atlas 4340 is an alternative to atlas 6582 throughhardening steel and to jis. It was very common in the early stages that the bars. Here are 7 ways that steel can fail as a result of quench cracking from heat treatment. It is ideal for achieving the required strength and hardness properties on many alloys.
If quench uniformity is required, such as in complying with the caterpillar 1e0106a or 1e0106b specification, polymer quenching. Overviewofthemechanismsoffailure in heat treated steel. Welding is not recommended because of the danger of quench cracking. I am going to post this i think i know what the issue was but would like some other input. Alloy depletion quench cracking heat treatment defects alloy depletion quench cracking heat treatment defects alloy depletion in aisi 4140 steel heat treatment defects alloy inclusion defects quench cracking heat treatment defects alloy inclusion defects quench cracking. John if you are doing a lot of tool making, a copy of the asm heat treaters guide would be a good investment since it does give a lot of charts and graphs showning hardness vs tempering temperature for hundreds of grades, including 4340, 4140 and the other tooling grades. The tempering process is an essential stage in heat treatment, especially in very fast cooling, as it brings back ductility. In your case i recommend using 4340 and getting it heat treated, as it will be 3x stronger than any of the three untreated. Quench cracking in steel as a case of hydrogen embrittlement. Bluewater thermal solutions hardening process enlists a wide variety of heat treatment techniques designed to increase the hardness, strength, and fatigue life of metal parts and components. Ask the ht shop to do a salt bath heat and quench, followed with a salt bath temper to 40 c rockwell hardness. Introduction during heat treatment of steel gears, thermal gradient, phase transformation, and the resultant internal stress interact with each other to contribute to distortion.
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