30CrNiMo Alloy Steel Hammer

Why use 30CrNiMo alloy steel to cast hammer?

Hammer is the main wear parts for shredder plant, hammer mill, and hammer crusher. The standard material for the hammer is manganese steel. However, manganese steel hammer does not have a good working life in crushing some material. Such as, In the thermal power industry, the Mn14 hammer can only operate for more than 100 hours on site. Therefore, in the specific environment of materials, how to improve the service life of hammers, reduce the consumption of metal materials, and reduce the frequent replacement of hammers on-site is studied. Increasing production is of great practical significance.

30crnimo is a kind of wear-resistant, high strength, and high toughness alloy with high initial hardness, so we use 30CrNiMo alloy steel to cast the hammer.

 

Characteristics of hammer abrasive wear

After the material enters the hammer working area, it is broken by the impact. Due to the reaction of materials. The material is broken by local force. The friction at the castor bar produces a crushing effect. The material is discharged from the gap of the grate plate. The whole crushing process is actually multiple and continuous impact crushing. The crushing ratio is more serious by impact crushing.

It can be seen from the hammerhead residue of the unloader after wear. The working face of the hammer is worn smooth. Through careful observation, we can see a fine wear line, about 10 mm long. Some streamlines are covered by other streamlines, just as the hammer is repeatedly in the sand, and the direction of the streamlines is consistent with the movement track of the hammer.

Because the hammer works with the main shaft of the crusher. Under the condition of high-speed rotation, the cement clinker is squeezed to both ends of the crusher wall by the moving hammers, resulting in the distribution of abrasives being low in the middle and high on both sides. Therefore, the hammers installed at both ends of the crusher in the same group wear faster than the hammers in the middle. Even if the hammers at both ends are against the wall of the crusher, the wear is more severe.

 

Relationship between material properties and wear resistance of hammer

Hardness

Hardness is an important factor affecting the abrasive wear resistance of steel. It is found from the test results that for the same material, the toughness is similar, the hardness is different, and the wear resistance of the hammer is also different. See the table below.

Material	Hardness(HRC)	Working days(day)	Output(ton)
70Mn2MoRe	54.4	30	1763
70Mn2Mo	42	13	846.3

 

Toughness

At present, the toughness of wear-resistant alloy cast steel is mainly expressed by AK value in China. We choose hammers with the same hardness but different impact toughness. It can be seen that the wear resistance of the material increases with the increase of AK value. See the figure below：

The results show that the HRC of 30crninmore, 30CrMnMo, and 50mn2 are 49 ～ 50, the AK value of 30crninmore is high, and the wear resistance is also the best.

 

30CrNiMo alloy steel hammer chemical composition

C	Si	Mn	Ni	P	S	Cr	Mo
0.26 – 0.34	max 0.4	0.5 – 0.8	1.8 – 2.2	max 0.025	max 0.035	1.8 – 2.2	0.3 – 0.5

Nickel in structural steel is to improve hardenability and toughness. The effect of nickel combined with chromium on hardenability is very strong, far more than that of two elements added alone. However, the important disadvantage of chromium-nickel steel is that it is very sensitive to temper brittleness, which can be overcome by adding platinum. Adding a certain amount of rare earth into the alloy cast steel can refine the structure of the steel, purify the grain boundary and improve the inclusions, so as to improve the impact toughness and castability of the steel. Compared with other steels, Cr Ni Pt re steel is a kind of wear-resistant material with high hardenability, high strength, and high toughness.

30CrNiMo alloy steel hammer heat treatment

The performance under different heat treatment conditions is shown in the table below：

Item	Heat treatment status	Hardness (HRC)	Ak value
Sample 1	Normalizing at 920 ℃	26	2.1
Sample 2	920 ℃ quenching + 300 ℃ tempering	47	4.87
Sample 3	920 ℃ quenching	50/51	3.7
Sample 4	880 ℃ normalizing + quenching 920 ℃	48/49	4.5
Sample 5	9O0 ℃/3N quenching + 200 ℃/6N tempering	49/50	6.5

 

Relationship between tempering temperature and hardness

Relationship between tempering temperature and hardness， which check in the following picture:

 

Compare with other materials hammer

In order to test 30CrNiMo alloy steel hammer quality, we also manufacture some hammers with other materials to compare the working life.

Item	Chemical Composition									Heat Treatment	Hardness (HRC)	Ak
	C	Mn	Si	Cr	Ni	Mo	P	S	Re
30CrNiMo	0.3	0.65	0.35	0.69	1.76	0.27	0.01	0.012	0.03	Water quenching + tempering	49.5	6.5
70MnMoRe	0.68	1.52	0.35			0.31	0.015	0.017	0.05	Oil quenching + tempering	54.4	3.2
30SiMnMo	0.37	1.56	1.22			0.25	0.015	0.008		Water quenching + tempering	50	2.3
70Mn2Mo	0.68	1.48	0.3			0.21	0.024	0.018		Fog cooling + tempering	42	3
50Mn	0.5	1.62	0.25				0.013	0.02		Water quenching + tempering	49	1
30CrNiMn	0.32	1.05	0.38	0.89		0.35	0.015	0.009		Water quenching + tempering	40	5.5
Mn14	1.21	13.59	0.52				0.067	0.008		Water toughening treatment	19.5	19

 

Different material hammer test results:

 

The results

1. 30crnimo is a kind of wear-resistant material with high initial hardness, good wear resistance, and high toughness. Through the comparative test of different materials. It shows good wear resistance on broken cement clinker. And the production process is simple, safe, and reliable.
2. 30CrNiMo alloy steel hammer span life 3.3 times than normal manganese steel hammer, It reduces the cost, reduces the labor intensity on site, increases the output, and has a considerable economic effect.