Certain highhardenability materials, such as 4340, are particularly prone to quench cracking and must be tempered immediately usually within 15 minutes of quenching to avoid problems. If a heavier liquid feed such as naphtha is used, the cracked gas is cooled with quench oil before entering the primary fractionator. However, as in motor shaft applications, under quenching and tempering conditions, 4340 steel typically use high preheating in low hydrogen processes. However, when steel parts fail, the consequences are dire. Interrupted quenching of steels typically in a molten salt bath, at a temperature just above the martensitic phase. Steam cracking quench process overview after the cracked gas leaves the transfer line exchanger, it needs to be cooled down further before it can be fed downstream to the separation columns. Throughhardening low alloy steel bar 4340 colour code. Usually it does not machine well, being gummy and leaves a rough surface. Material and process selection can contribute to cracking as well. What happens to the physical size of 4340 during heat treating.
The purpose is to delay the cooling for a length of time to equalise the temperature throughout the piece. Evaluation of toughness in aisi 4340 alloy steel austenitized at low and high temperatures robert o. I should have used the oil quench tank to cool it off faster, but there was a reason i didnt. Any condition that concentrates the stresses encountered in quenching will promote the formation of quench cracks e. Overheating during the austenitizing portion of the heat treatment cycle can. Not much practical use other than being a feedstock for heat treating. 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. Quench relaxing signals from the album conse quench ial. It is an alloy structural grade which used by the sae internationalsae, and it is chromenickel low alloy steel. I quenched and tempered the big 4340 beast, then had to wait a long time for it to cool down so i could use our portable brinell tester. Overviewofthemechanismsoffailure in heat treated steel.
Quench cracks 3 ways to recognize speaking of precision. Us4404047a process for the improved heat treatment of steels using direct electrical resistance heating. Marquench hardening available in salttosalt or furnacetosalt. This will minimise distortion, cracking and residual stress. For chisels, take it to a straw to bronze color and quench. Stress corrosion cracking of highstrength steels uq espace. This increased strength makes austempered steel ideal for applications where. Quench ing, therefore, is a very important process in the successful hardening of commercial heat treaters have not received any specific mandates from industry or government agencies to modernize their heat treating equip ment. Fatigue precracking was performed using either a 300,000 lb capacity mts. Aisi 4340 steel is a medium carbon, low alloy steel known for its toughness and strength in relatively large sections.
And it has good toughness, fatigue resistance, impact toughness and etc. The crack is seen to travel along the prior austenite grain boundaries. Us4404047a process for the improved heat treatment of. According to the actual production situation, we believe that the main reason of quenching crack of 4140 steel plate is. This grade is not considered weldable by standard methods but it can be welded by more sophisticated methods such as ebw. Quench cracking in steel as a case of hydrogen embrittlement.
The quench andtemper process induces enormous stresses, which can lead to part cracking during the process if good part design guidelines and proper heat treating practices are not followed. Continuous mesh belt or roller hearth furnaces with oil or water quench. Further, the surface hardening of steel can have an advantage over through hardening. Here are seven ways that steel can fail as a result of quench cracking from heat treatment. Quench hardening is a mechanical process in which steel and castiron alloys are strengthened and hardened. The martensitic transformation starts at the outermost surfaces of the part being quenched. Failures of steel parts in service or production occur very infrequently.
Aisi 4340 alloy steel as a function of tempering tem. Pdf improved production of automotive parts by intensive quench. Hence, thegeneralruleofquenchingfromjustabovethecriticalrange. For materials such as 4340, tempering must take place within 15 minutes of removal from the quench to avoid quench cracking. This material at my shop is quenched in 250f agitated oil without any issues.
Lower bainite is more resistant to crack formation as indicated by higher finite life fatigue strength. Seven causes for quench cracking in steel failures of steel parts in service or production occur infrequently. Overload failure of a quenchcracked aisi 4340 steel. Normal ranges of mechanical properties corresponding to a specific hardness are listed below. Sae aisi 4340 steel properties, heat treatment, equivalent. Preheating and postweld heat treatment is desirable to prevent cracking and compromised mechanical properties. 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.
In this case, maintenance and inspection personnel failed to detect a fatigue crack in the compressor stage of an aircraft engine. Quenching and tempering provides steel with high strength and ductility. 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. The high hardness of 4340 alloy steel requires that the material be welded in the annealed or tempered state and then heat treated to resist martensite formation and cold cracking. Because there are high capital expenditures involved with the installa. Troubleshooting and prevention of cracking in induction hardening. I have some shafts to machine from 4340 512 dia stock, to an average size of 5. C, followed by slow cooling no quench reducing the problem of distortion. The quench cracking that occurs in steels with carbon contents greater than about 0. Quench cracking of steel cracking resulting from stresses produced during the austenite to martensite transformation during heat treating quenching and tempering.
We will not be discussing the metallurgical properties of 4140 or trying to explain what happens to its microstructure when it cools too rapidly, just remember that the key is to control our cooling rate. Jade band marigold introduction atlas 4340 is a nominally 1. A comparison of fatigue properties of austempered versus. This is to reduce likelihood of cracking during quench. Effective and economical prevention of quench cracking. Quench crack in aisi 4340 steel heat treatment defects quench crack in aisi 5160 part heat treatment defects quench crack in w2 waterhardening part heat treatment. Presumably the stresses produced by the faster quenching the latter case are greater than in the. Introduction during heat treatment of steel gears, thermal gradient, phase transformation, and the resultant internal stress interact with each other to contribute to distortion and residual stress in the quench. Our largest furnace is capable of performing oil quench hardening with internal working dimensions of 36w x 72l x 42h.
Nitriding is carried out at 490 o c 530 o c, followed by slow cooling no quench reducing the problem of distortion. Ive made hammers out of 4340 and tempered them by running the color and quenching in oil. Server it has been reported for asquenched aisi 4340 steel that high temperature austenitizing. Ef fective and economical prevention of quench cracking. Typical heat treatment defects of gears and solutions. Certain highhardenability materials, such as 4340, are particularly prone to quench cracking and must be tempered immediately usually within. 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. 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. External corners need to at least be broken before heat treat, as they too are a stress concentration area. Here are 7 ways that steel can fail as a result of quench cracking from heat treatment. 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. I even made a larger hand hammer out of 4140 since this has happened and did a full quench on it and it didnt crack.
Quench andtempering 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. The present invention virtually eliminates the problem of quench cracking and minimizes quench distortion as well as providing a finished product with improved uniformity, improved surface quality, and improved mechanical properties. Heat treating and brine quench of prepost machined 4340. Quenching is a stage of material processing through which a metal is quickly brought down to room temperature from a high temperature by rapid cooling. In the quenching action, the steel is subject to nonuniform cooling, thermal deformation, and a phased grain transformation that can. It is important to learn that crack initiation within the heattreated components, its growth, and propagation is affected by a number of factors. Aisi 4340 is also one kind of nickel chromium molybdenum steels. For hammers, quench just as the color purple creeps up to the face. It can be avoided by first plating the steel with nickel. How to quenching and tempering of 4140 alloy steel. Upon application of power, the compressor stage ruptured, with shrapnel severing fuel. Heat treating and brine quench of prepost machined 4340 nickel alloy steel.