Hardening and tempering furnace for steel grade SC45 and 40CR

Hardening and tempering furnace for steel grade SC45 and 40CR

   In the heat treatment factory or small mechanical factory, hardening and tempering plays an important role in the working. Hardening and tempering is conventional heat treatment, but to stabilize the quality is still difficult. To ensure the quality of the parts after hardening and tempering, how to make sure the conduction of heat treatment process is an important factor. According to years of operating practice, we are sharing some ideas for hardening and tempering SC45 and 40Cr.

   Hardening and tempering is a double heat treatment with quenching and high temperature tempering, and its purpose is to make the workpiece have good comprehensive mechanical properties.

   Quenched steel has carbon quenched and tempered steel and alloy quenched and tempered, whether it is carbon steel or alloy steel, its carbon content control is strict. If the carbon content is too high, the strength of the workpiece is high, but the toughness is not enough; if carbon content is too low, toughness increased but strength is not enough. In order to get a good overall performance for the parts, the carbon content is generally controlled at 0.30 ~ 0.50%.

  When hardening, whole section need to be hardened, which can make the parts get fine needle-like quenched martensite-based microstructure. Through the high temperature tempering, the parts can get uniform tempered sorbite-based microstructure. Small factories can not do metallographic analysis for each lot, generally only do the hardness test, which means that the material hardness must get material quenching hardness after quenching.

The operation of material hardening and tempering must be strictly conducted in accordance with the process file, we can only give ideasa for how to achieve the process during operation.

1. SC45 HARDENING AND TEMPERING

    SC45 steel is carbon structural steel, hot and cold processing performance are good, the mechanical performance is good. And the price is low and easily to get, so it has widely used different industries. Its biggest weakness is the hardenability is low, which is not suitable for cross-sectional size and high requirement parts..
 
     SC45 steel quenching temperature is in A3 + (30 ~ 50) ℃, in practice, generally take the upper limit. High quenching temperature can increase the workpiece heating speed, reduce surface oxidation and improve work efficiency. In order to homogenize the austenite of the workpiece, a sufficient holding time is required. If the actual installed capacity is large, you need to extend the insulation time. Otherwise, it may have the phenomenon of insufficient hardness due to ununiform heating. But the insulation time is too long, there will be thick grain and more oxidation skin. We believe that if the furnace installed capacity is greater than the provisions of the process, heating an holding time should be extended 1 /5.

Because SC45 steel hardenability is low, so we should use the cooling rate of  more than 10% brine solution. After the workpiece into the water, it should be hardened, but not cold. If the workpiece cold in the brine, it is possible to crack. This is because when the workpiece cooled to about 180 ℃, the structure stress will lead to it caused by austenite quickly transformed into martensite. Therefore, when the parts cold to this temperature, we should adopt slow cooling method. As the water temperature is difficult to master,we should operate as per experience.  when the water in the workpiece jitter stop, we can take out the parts (oil cool will be better). 

The hardness of SC45 after hardening should reach HRC56 ~ 59, the large section maybe lower, but not lower than the HRC48. Otherwise, it shows that the workpiece is not fully quenched, the organization may appear sorbite or even ferrite organization. Thoutough tempering, this organization still remain in the matrix,will not achieve the purpose of hardening and tempering.

 After hardening, the temperature for high tempering will be 560 ~ 600 ℃, hardness requirements is HRC22 ~ 34. As the purpose of hardening and tempering is to get comprehensive mechanical properties, the hardness range is wide. But the drawings have hardness requirements, it is necessary to adjust the tempered temperature according to the drawings to ensure the hardness. If some shaft parts require high strength, hardness requirements will be high; and some gears need milling after hardening and tempering, so the hardness requirement is lower. About the holding time for tempering, we should decide as per parts size and hardness requirements. For the heating time and heating temperature, we can set corresponding parameters for the hardening and tempering furnace.

2. 40Cr STEEL HARDENING AND TEMPERING TREATMENT

   40Cr can increase the hardenability of steel, improve the strength of steel and tempering stability, which has excellent mechanical properties. Larger section or important parts, we should use Cr steel. But Cr steel has second type temper brittleness.

The process parameters cards have rules for 40Cr parts hardening and tempering, we understand in the actual operation :
 
(A) 40Cr parts ahould adopts oil cooling after quenching: 40Cr steel hardenability is better, the deformation will be small if cooling in the oil. However, small enterprises in the case of tight supply, they will not adopt oil cooling for some simple parts. They use water for cooling and not find cracking. But the operator should master the water temperature as per experience.

(B) 40Cr parts hardness is still high after hardening and tempering, the second tempering should increase by 20 ~ 50 ℃, otherwise, the hardness reduction is difficult.

(C) After high temperature tempering, complex shapes of parts should be cooled in the oil, simple parts can be cooled in the water. The purpose is to avoid the effect by second tempering brittleness. The parts treated by fast cooling, the stress should be relieve if necessary

YuanTuo has 13 years of experience in the design and production of quenching and tempering furnace for various grades of steel, knowing different heat treatment requirement for different steel, we can help you to choose suitable quenching and tempering furnace.

Contact person: Tom Wang

Email:yuantuodianlu@163.com

Phone: 0086-13303078975(whatsapp, wechat,line )

Specialist of billet heating furnace and system in China; Glad to be your business partner in induction heating field.