27SiMn tempered seamless steel pipe for hydraulic prop

The effect of tempering process on the comprehensive mechanical properties of 27SiMn seamless steel tubes for hydraulic props was studied. The results show that the yield strength and tensile strength of the tested steel tend to decrease while the elongation and reduction of area increase with the increase of tempering temperature during tempering at 520-640 t ; When fired, the surface Brinell hardness HBW of the test steel is between 250 and 267 , meeting the target value requirements. The results of industrial trial production and mass production show that the comprehensive mechanical properties of steel pipes after 580 t tempering all meet the requirements of users.
Key words: 27SiMn ; tempering; surface Brinell hardness

27SiMn hot-rolled seamless steel pipe for hydraulic props is the base material of hydraulic equipment cylinders and columns, and is widely used in various industries such as coal mines and large machinery. According to the requirements of GB/T 17396-2009 , there are three delivery states of steel pipes: rolled state, annealed state, and quenched and tempered state . In terms of mining hydraulic supports and other hydraulic frames, 27SiMn needs to be quenched and tempered. Only when the design requirements are met can it be used. With the increase of the load bearing capacity of the hydraulic prop, users have put forward higher requirements for the strength and toughness of the steel pipe, especially for the Brinell hardness HBW of the surface of the steel pipe after quenching and tempering .

27SiMn  Overview
In recent years, large-scale coal mining machinery production bases such as Beimeiji, Zhengmeiji and China Shipbuilding Industry have put forward higher requirements for hot-rolled seamless steel pipes for 27SiMn hydraulic props. Users require that the comprehensive mechanical properties of steel pipes after quenching and tempering reach The following target values: tensile strength Rm3800 MPa, yield strength Rp0 , 24600 MPa, elongation A M 17 % , reduction of area ZM 45 % , impact energy ( V - notch at room temperature ) A kv2 M 50 J, after quenching and tempering , the matrix hardness HBW is 235-280 .

Standard requirements are: tensile strength R m ≤ 980 MPa , yield strength R p0.2 m 835 MPa , elongation A M 12 % , reduction of area Z M 40 % , impact energy ( V -shaped notch at room temperature) A kv2 M 39 J, matrix hardness HBW after quenching and tempering is not less than 217 unloading . For 27SiMn 4 supplied according to standard requirements , Baotou Steel Seamless Steel Tube Factory has a mature heat treatment process, but has never studied the production of 27SiMn by heat treatment according to the performance required by the above-mentioned users . Therefore, this article takes the 27SiMn hot-rolled seamless steel pipes for hydraulic props with specifications of ①194 mm X 19 mm produced by Baotou Steel Seamless Steel Tube Factory as the research object, and mainly studies the tempering temperature.
Table 1 The influence of temperature on the comprehensive performance of steel pipes. It is expected to provide experimental and theoretical guidance for the industrial mass production of 27SiMn hydraulic prop hot-rolled seamless steel pipes according to user requirements through experimental research.
2 Experimental materials and methods
27SiMn steel Experimental materials
The chemical composition of the steel used in the experiment meets the chemical composition requirements of the national standard for 27SiMn steel, and its chemical composition requirements for 27SiMn steel are shown in Table 1 .

C	Si	Mn	P	S	Cr	Ni	Cu	Mo
0.24 -0.32	1.10 -1.40	1.10 -1.40	W0.035	W0.035	W0.30	W0.30	W0.20	W0.15

27SiMn steel Mechanical properties of industrial trial steel pipes

batch number	parts	Yield Strength	tensile strength	Elongation	section Shrinkage /%
		/MPa	/MPa	/%
12-09-395	head	717	888	18 . 5	54
	tail	687	872	21 . 0	58
12-09-387	head	760	939	22 . 0	57
	tail	692	887	18 . 5	52

27SiMn steel in conclusion:
( 1 ) The tempering temperature has an important influence on the surface Brinell hardness of the steel pipe. When the tempering temperature is higher than 560 t , as the tempering temperature increases, the surface Brinell hardness of the test steel shows a downward trend. When the tempering temperature rises to 620-640 t , the surface Brinell hardness of the test steel One of the hardness values is 232 , which is lower than the target value; when the tempering temperature is lower than 560 t (inclusive), the Brinell hardness values of the test steels are all above 300 , exceeding the upper limit required by the target value. Therefore, the tempering temperature that meets the surface Brinell hardness requirements should be in the range of 560-600 t .

1. The experimental research results show that after holding at 920 t for 60 minutes , water quenching + 580 t for 70 minutes and air cooling, the comprehensive mechanical properties of the experimental steel meet the requirements of users .
2. The results of industrial trial production and mass production show that the optimal heat treatment process obtained through experimental research can ensure that the comprehensive mechanical properties of steel pipes of different specifications meet user requirements. Through experimental research and industrial production instructions, the optimal heat treatment process obtained in this article can provide guidance for on-site mass production.

---