The M designator is a "Mandatory Classification Designator" that indicates that the electrode meets the US military requirements (MIL Spec.)– see ASME Section II Part C, SFA-5.1 figure 10. These are more stringent than typical commercial requirements. The Level 1 indicates the testing level within the applicable MIL Spec. See the following.
Hope this helps/answers your question.
From SFA 5.1 Annex A:
A7.6.8 E7018M [E4918M] Classification
A7.6.8.1 E7018M [E4918M] electrodes are similar to E7018-1H4R [E4918-1H4R] electrodes, except that the testing for mechanical properties and for classification is done on a groove weld that has a 60° included angle and, for electrodes up to 5/32 in [4.0 mm], welded in the vertical position with upward progression. The impact test results are evaluated using all five test values and higher values are required at –20°F [–30°C]. The maximum allowable moisture in-coating values in the "as-received" or reconditioned state are more restrictive than that required for E7018R [E4918R]. This classification closely corresponds to MIL-7018-M in the United States military standard MIL-E22200/10 specification, with the exception that the absorbed moisture limits on the electrode covering and the diffusible hydrogen limits on the weld metal are not as restrictive as those in MIL-E-22200/10.
A7.6.8.2 E7018M [E4918M] is intended to be used with dcep type current in order to produce the optimum mechanical properties. However, if the manufacturer desires, the electrode may also be classified as E7018 [E4918] provided all the requirements of E7018 [E4918] are met.
A7.6.8.3 In addition to their use on carbon steel, the E7018M [E4918M] electrodes are used for joining carbon steel to high-strength low-alloy steels and higher carbon steels. Fillet welds made in the horizontal and flat welding positions have a slightly convex weld face, with a smooth and finely rippled surface. The electrodes are characterized by a smooth, quiet arc, very low spatter, and medium arc penetration.
From the classification document (SFA-5.1 proper)
Table 3.
Table 10 for limit of moisture content % - as received/conditioned and as exposed
Table 11
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of 4wheels
Sent: Thursday, July 20, 2017 7:14 PM
To: Materials & Welding
Subject: [MW:26679] 7018
Hello,
What is the difference between 7018 and 7018m?
Also, I see on ebay rods that are 7018m have a designation of level 1 - what is the level 1?
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